An amount of information circulating in a network in an enterprise has been increasing year by year, and an importance of a communication service for an enterprise user has been more and more enhanced. In accordance with the situation, a communication common carrier provides a virtual dedicated line service to an enterprise user as an object by laying a communication network for connecting LAN's in an enterprise which are arranged at plural key points.
In a communication service for an enterprise user as an object, a high reliability is requested in order to firmly carry out a communication of important data. Hence, attention is paid to T-MPLS realizing to assure a band by establishing a path previously ensured with the band from end to end.
T-MPLS is a kind of an MPLS (Multi Protocol Label Switching) technology providing a label to an IP packet, and transferring the IP packet by referring to the label. A communication network applied with T-MPLS (hereinafter, T-MPLS network) accommodates plural access networks and provides a communication service between LAN's in an enterprise connected to the access networks. The T-MPLS network is constituted by an edge node accommodating the access network at an edge and a core node carrying out a process of assorting frames gathered from the plural edge nodes. A person operating the T-MPLS network sets and monitors a path accommodated by the T-MPLS network by using NMS (Network Management System).
The edge node sets color information (green or yellow or red) described in J. Hinanen, R. Guerin, “A Two Rate Three Color Marker”, IETF RFC2698 September, 1999 to a frame flowing in from the access network. The color information represents a priority of transferring the frame, showing that green has the highest priority and red has the lowest priority. The edge node as well as the core node predominantly transfers a frame having a high priority by referring to the color information set to the frame. Specifically, the edge node as well as the core node transfer a frame set with green (hereinafter, green frame) more predominantly than a frame set with yellow (hereinafter, yellow frame). Further, the edge node as well as the core node transfer the yellow frame more predominantly than a frame set with red (hereinafter, red frame). Further, the core node carries out a process of transferring a frame without updating the color information in the frame so as to restrain a load in order to process enormous traffic gathered from a number of the edge nodes.
As a technology of transferring a frame in accordance with color information, a technology described in JP-A-2008-294535 provides color information in accordance with an inflowing band (INR) and determines whether the frame is to be transferred or abandoned based on the color information and a situation of vacancy of a frame processing buffer within the same node. The technology previously sets a minimum assurance band (CIR) and a maximum assurance band (PIR) for each path, and sets green in a case of INR<CIR, yellow in a case of CIR<INR<PIR, and red in a case of PIR<INR. The node transfers the green frame and abandons the red frame. Further, the technology sets a priority previously to a path, transfers the yellow frame when the buffer is vacant, transfers only the yellow frame of a high priority path, and abandons the yellow frame of a low priority path when the buffer is crowded.